IS 4453: Subsurface Exploration by Pits, Trenches, Drifts and Shafts - Code of Practice

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IS 4453 (2009) : Subsurface Exploration by Pits, Trenches,
Drifts and Shafts - Code of Practice [WRD 5: Gelogical
Investigation and Subsurface Exploration]

Satyanarayan Gangaram Pitroda
Invent a New India Using Knowledge

Bhartrhari — Nitisatakam
"Knowledge is such a treasure which cannot be stolen"

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PROTECTED BY COPYRIGHT

IS 4453 : 2009

(Reffirmed-2012)

f ^YM f^SM )

Indian Standard

SUBSURFACE EXPLORATION BY PITS, TRENCHES,
DRIFTS AND SHAFTS — CODE OF PRACTICE

( Second Revision )

ICS 93.020

O BIS 2009

BUREAU OF INDIAN STANDARDS

MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

June 2009 . Price tJroup 4

Geological Investigations and Subsurface Exploration Sectional Committee, WRD 05

FOREWORD

This Indian Standard (Second Revision) was adopted by the Bureau of Indian Standards, after the draft finalized
by the Geological Investigations and Subsurface Exploration Sectional Committee had been approved by the
Water Resources Division Council.

This standard was first published in 1 967 and revised in 1 980. The present revision is proposed to reflect the
experience gained on the subject since then.

Open test pits, trenches, drifts and shafts are features accessible for visual examination in subsurface exploration
and afford complete information on the ground penetrated. Location and depth of pits, trenches, drifts and shafts
depend on the investigation requirement and the type of proposed structure. For water resources projects, location
and depth of subsurface exploration by pits, trenches, drifts and shafts is of paramount importance and may be
decided in consultation with engineering geologist. Knowledge of the nature, structure and composition of the
strata encountered is obtained by inspection of the materials in place. They are useful features for foundation
exploration, wherever the depth of overburden and ground water conditions permit.

For exploring foundations for dams and prospecting for embankment material or concrete aggregates, open pits
and trenches are generally einployed to obtain the required information. They enable selective and controlled
sampling for laboratory tests and classification of the excavated material.

Drifts are normally employed to explore, in detail, in the hill-sides, the continuity, nature and structure of particular
geological formations. They are most frequently used for establishing the minimum excavation limits to reach
fresh and sound rock in order to decide the foundation level of the structures like dams, spillways, etc, and to
have access to the proposed locations of underground structures (tunnel, caverns, etc) for site specific geotechnical
assessment and also for the detailed investigation of fault or shear zones as well as other zones of weakness and
buried channels in the river section. Drifts are specially useful for taking undisturbed samples for tests in the
laboratory and for performing in-situ tests, like the uniaxial jacking test, in-situ shear test on rock mass and other
tests to determine modulus of deformation, shear strength parameter and in-situ stress measurement of the
formations encountered.

Shafts are normally employed to vertically reach either a particular formation at a great depth (exceeding about
6 m) or to extend the exploration below river bed by means of tunnels.

It has been assumed in the formulation of this standard that the execution of its provisions is entrusted to
appropriately qualified and experienced people, for whose guidance it has been prepared.

For the purpose of deciding whether a parficular requirement of this standard is complied with, the final value,
observed or calculated, expressing the results of a test or analysis, shall be rounded off in accordance with
IS 2 : 1960 'Rules for rounding off numerical values (revised)' . The number of significant places retained in the
rounded off value should be the same as that of the specified value in this standard.

IS 4453 : 2009

Indian Standard

SUBSURFACE EXPLORATION BY PITS, TRENCHES,
DRIFTS AND SHAFTS — CODE OF PRACTICE

( Second Revision )

IS No.

1498

1970

1892

1979

3764

1992

1 SCOPE

This standard lays down the method for subsurface
exploration by means of pits, trenches, drifts and shafts.

2 REFERENCES

The following standards contain provisions which,
through reference in this text, constitute provisions of
this standard. At the time of publication, the editions
indicated were valid. All standards are subject to
revision and parties to agreements based on this
standard are encouraged to investigate the possibility
of applying the most recent editions of the standards
indicated below:

Title
Classification and identification of
soils for general engineering
purposes {first revision)
Code of practice for subsurface
investigations for foundations (first
revision)

Code of safety for excavation work
(first revision)

3 EXPLORATION BY TEST PITS

3.1 Pits are dug manually but mechanical equipment
may also be used. The depth of the pit should be
according to the requirements of investigation and is
generally limited to a few metres below the ground
water table (see IS 1 892). For carrying out excavation
safely, reference may be made to IS 3764. Pits are
normally of the shape of an inverted frustum of a
pyramid. The top of the pit is usually a square of size
3 m X 3 m and its bottom is also a square of 1 .2 m x

1.2 m providing sufficient space. The depths of such
pits are around 3 m in softer soil with sloping cut walls.
The walls may be kept near vertical in case of hard
soil and the depth of the pit may also be increased to
6 m. Additional space for sheeting and supports,
hoisting arrangements, ladder, in-situ tests, sampling
for laboratory tests, etc, should be provided {see Fig. 1 ).

3.2 During excavation, the bottom of the pit should be
kept at a level so that each lift may represent the
corresponding portion of the deposit in quality and
quantity. The excavated material should be placed round
the pits as stockpiles, separated when significantly

SECTION XX

so mm SHEETINO

IFACE

-j!5ss:

150 X ISO mm STUO FRAUES
TO BE SPACED AS NATURE
OF OROUNO REQUIRES

NSURFAC

a

E 5

SI

"1

: J^

a:

IE

'H-

FiG. 1 Typical Test Pit Showing Arrangement of
Sheeting and Bracing (Illustrative Sketch)

different materials are encountered, and marked stakes
should be driven into the stockpiles to indicate the
depth from which the materials were excavated in order
to facilitate logging and sampling later on. Based on
design requirements, SPT tests wherever required, may
also be conducted at regular intervals of 1 .0 m to 1 .5
m at the change of the strata for determination of
potentiability of liquefaction of material and modeling
of deformation.

3.3 Deep test pits should be ventilated to prevent
accumulation of dead air. For this purpose connected
lengths of pipe starting slightly above the floor and
extending about one metre above the mouth of the pit

IS 4453 : 2009

have been found satisfactory. Canvas sheeting may also
be used to deflect wind into the pit. When there is
likelihood of the presence of obnoxious gases, special
precautions shall be taken for ventilating the pit
{see IS 3764). To prevent accumulation of dead air,
forced ventilation may be necessary,

3.4 Test pits left open for inspection shall be provided
with covers or barricades for safety. Pits and trenches
shall be suitably fenced. Trenches and pits should be
filled back properly, when exploration and physical
inspections are completed and the relevant records have
been obtained.

3.5 When water is encountered in a pit, a suitable
dewatering system may be required for further
progress. Where suction pumps are used, it is desirable
that the suction hose be 10 mm larger in diameter than
the discharge opening of the pump and the suction head
not more than 4.5 m. This requires resetting the pump
in the pit (on a frame attached to the cribbing) at
intervals of about 3.5 m. When an internal combustion
engine is used in the pit, it would be necessary to lead
the exhaust gases well away from the pit.

3.6 Undisturbed samples may be obtained from open
pits from each stratum if the nature of the deposit
permits. For this purpose, a pillar of suitable
dimensions, say, 40 cm x 40 cm should be left
undisturbed at the centre of the pit to collect
undisturbed samples of required size from each layer
showing a change of formation. If the thic kness of each
layer exceeds 2 m, a second sample may be taken.
These undisturbed samples will be useful for the
determination of several characteristics of the in-situ
materials. Special care shall be taken to preserve the
natural moisture content of the samples.

4 EXPLORATION BY TRENCHES

4.1 Trenches are similar to test pits in all respects,
except that they are continuous over a length and
provide a continuous exposure of the surface along a
desired line or section. They are best suited for
exploration on slopes,

4.2 The field work consists of excavating an open
trench from the top to the bottom of the slope to reach
representative undisturbed material. Either a single slot
trench down the face of the slope or a series of short
trenches spaced at appropriate intervals along the slope
may be excavated. Depending on the extent of the
investigation required, use may be made of picks and
shovels, bulldozers, ditching machines, back hoes or
dragline. A trenching layout suitable for materials
investigations is shown in Fig. 2.

4.3 Safety precautions shall be taken as in the case of

deep test pits to prevent accidents caused by caving
ground {see IS 3764).

4.4 All the instructions for pits given in 3 shall apply
to trenches.

5 EXPLORATION BY DRIFTS OR TEST

TUNNELS

5.1 Drifts or test tunnels should be provided with a
gentle/low outward slope of the floor in order to be
self-draining. A rectangular section with minimum
clear dimensions of 1,8 m width and 2.1 m height is
adopted in hard rock. In soft rock, however, it will be
advantageous to provide an arched roof with the
dimensions as above.

5.2 The roof and the sides shall be adequately
supported, wherever the ground is unable to stand. The
size and spacing of the supports will depend on the
character of the formation and the spacing and attitude
of joints therein. Wherever blocky and hard rock is to
be tunneled through, it may be advantageous to use
rock bolts to hold together the jointed blocks of rock.

5.3 Ventilation by air from a compressor or a blower
depending on the length of the drift may be resorted to
for removing pockets of foul air or blast gases when
explosives are used,

5.4 Adequate lighting arrangement shall be provided
for proper examination and recording of data in drifts
or tunnels.

5.5 Proper approach to the drift shall be made for
proper transportation of men, testing equipment and
other materials/accessories. Proper ropeway shall be
provided for crossing the river for testing rock mass
on the other bank of the river.

6 EXPLORATION BY SHAFTS

6.1 Shafts may be rectangular or circular in section
depending upon the investigation requirement and the
ease of construction and should have minimum
dimension of 2.4 x. 2.4 m or of 2.4 m diameter in case
of circular section, to provide space for movement of
men, equipment and other accessories.

6.2 In hand dug shafts, the materials are removed by
buckets operated by hoists or windlass, which should
be equipped with a ratchet device for safety.

6.3 Deep shafts should be ventilated to prevent
accumulation of dead air or blast gases when explosives
are used. For this purpose, connected lengths of stove
pipe starting slightly above the floor and extending
one metre into open air above the mouth of the shaft
should be used. Air from a compressor or blower may
also be used.

SAMPLE

ORIGINAL GROUND SURFACE

w

3A HORIZONTAL OR MILDLY
SLOPING GROUND

-ORIGINAL GROUND
SURFACE

CHANGE OF
STRATA

BOTTOM OF
THE TRENCH

3B STEEPLY SLOPING GROUND

NUMBER OF SAMPLES TO SUIT
POSE OF INVESTIGATION

CHANGE OF STRATA

SIDE SLOPE TO SUIT
THE MATERIAL AND
DEPTH OF EXCAVATION

-COARSE SAND-

'■•■.•• AND- 6RAVE4.;\>-TT-r: — r - '■' ' ''^••:'\-:

..•■;*••.•■.■ .• *■•■ . A .. \^ ^j . — ^ A ■'...-•• \ .: .■v. .'.

BOTTOM WIDTH TO SUIT
THE METHOD OF EXCAVATION

SECTION XX

I

Fig. 2 Typical Trenching Layout (Illustrative)

184453:2009

6.4 When water is encountered, a pumping system
should be used to enable further progress. Electrical
pumps should be preferred to ones with internal
combustion engines to avoid pollution of air; otherwise
it would be necessary to lead the exhaust gases well
above the mouth of the shaft.

6.5 In weak and caving ground, the sides of the shafts
shall be adequately supported to prevent accidents. The
spacing and the size of the support will depend on the
nature of the strata.

6.6 Shafts left open for inspection shall be provided
with covers, grills or barricades for safety.

7 RECORDING OF INFORMATION

7.1 Besides proper supervision of the work, careful
and systematic records should be kept and made
available at project site for consultation. Inaccurate
observation and incomplete records may result in
serious errors of geological correlation of formations
and ineffective expenditure of time and money.

7.2 Test Pits

A recommended proforma for the recording of
information obtained from trial pits is given in Annex A.
In some cases, where the strata are irregular in shape, it
may be necessary to carry out three-dimensional logging
in die same manner as provided for shafts (,see 7.4).

7.3 Drifts

Geological logging and sampling of exploratory drifts
should proceed concurrently with the operation of
excavation, after proper cleaning of side walls and-
crowns. The drifts should be mapped showing the
geological formations indicating extent of weathering
and details of structural features, such as the direction
and magnitude of dip, extent and attitude of fault or
shear zones and clay seams. A longitudinal section of
a drift is given in Fig. 3. A three-dimensional geological
log is shown in Fig. 4. For preparing a three-
dimensional log of an exploratory drift, the perimeter
of the section is assumed to be opened out at the
junctions of invert and walls; walls and crown (spring
line) up to centre of crown so that the length of the
diagram represents the length of the drift to a suitable
scale and the width of the diagram represents the
perimeter to the same or other convenient scale. The
boundaries of geological units and weaker zones and
the trend of other geological features like joints,
beddings, foliations, etc, should be recorded In the
spread out section of the drift. This recording should
be done by measuring the distance of any particular
geological feature at the junction of the half-crown and
the wall, the spring line ( mid-point line of the wall)
and at the junction of the wall with the floor of the

drift. Before logging, the distances are usually marked
along the spring line (or centre line) of the drift, from
a reference point which is usually taken at the portal
of the drift, or at the starting point of the open-out
section of the drift, if any. The log of the drift ihus
obtained on a spread out section is folded back (to the
original rectangular shape of the drift) to give a three-
dimensional model of the drift, showing the actual
disposition of the geological features.

7.4 Shafts

The shafts are concurrently mapped with excavation
in the same way as drifts giving the type of rocks
encountered at various elevations, direction and
magnitude of dip, extent and attitude of bedding/folial
plane, fault or shear zones, clay seams, etc. For
preparing a three-dimensional (3D) log of a circular
shaft, the depths should be marked from the ground
level downwards, along four lines ( shown for one line
in Fig. 5 ); the north-south ( or upstream-downstream)
and east-west (or right-left) diameters of the shaft. The
perimeter of the shaft on any suitable scale should be
taken to have been spread out in the vertical plane
parallel to the east-west (or right-left) diameter of the
shaft and passing through the south (or downstream)
edge of the shaft, half of the spread out section lying
to the east (or right) side and the remaining half to the
west (or left) side. The intercepts of the various
geological features on the four reference lines should
be recorded on the spread-out log. When this log is
folded back to the circular shape, a three-dimensional
model of the exploratory shaft is obtained, showing
the actual disposition of the geological features. A
typical example of the plot of a three-dimensional log
for circular shaft is given in Fig. 5.

7.5 Plans and sections illustrating exploratory features
should generally be drawn to the scale of 1 : 1(X)0.
Geological logs should be drawn 1 : 100 scale. The
information given in 7.5.1 and 7.5.2 should also
recorded.

7.5.1 General

a) Organization responsible for the work.

b) Location on map — If a co-ordinate system
has been established the location should be
given by co-ordinates easting or northing or
chain stations. The location shall be defined
by the number of the exploratory feature, its
co-ordinates and elevation. In the case of
drifts, direction should also be mentioned. At
site a permanent pillar should be erected at
the portals of drifts and near the mouths of
pits with the grid co-ordinate lines and
number inscribed thereon.

c) Elevation of ground surface or other reference

IS 4453 : 2009

d)
e)

point — The elevation with respect to mean

sea level or reduced level, of the ground

surface and of the bottom or end of excavation

along with intermediate elevations and

corresponding depths from the top or start of

the excavation should be indicated for all

points of change of formation, to demarcate

the boundaries of different types of materials

penetrated.

Dates of starting and completing the work.

Name of persons responsible for the

preparation of plans and sections with

signature.

Scales of plans or sections in linear

representation.

g) On plans, the north point, either true or
magnetic, should clearly be marked.

7.5.2 Geotechnical Details

a) Soil or rock type should be recorded giving
brief, but complete description of the nature
and condition of the materials penetrated.
Different formations and their physical
condition should be shown by appropriate
symbols or colours.

b) Disposition and attitude of contacts, faults,
joints, shear zones and clay seams.

c) Inflows of water and ground water
fluctuations — Records should be kept
showing the elevation and fluctuations in

^ Orientation

5 6 7 8 9 10 11 12 13
REDUCED DISTANCE IN METRES

14 15 16 17 re

CLAY FILLED JOINT

SHEAR ZONE

MASSIVE LIME STONE

i;i;i;i highly BLOCKY lime STONE
THINLY BEDDED SLATES

E^g^l SILICEOUS SLATES

Bedding and Foliation DIPS : (Points 1 to 4 In the section)

1. At RD m dipping due .

2. At RD m dipping due .

3. At RD m dipping due .

4. At RD m dipping due .

Joints:

1 . Joint at RD .

2. Joint at RD .

3. Joint at RD .

. m dipping due .

. m dipping due .

. m dipping due .

RD = Reduced distance in metres.

NOTES

1 In addition details about otJier structural discontinuities lilce iiedding (5o), foliation (S,), Joints (7,) etc, should also be given on
the section.

2 Weathering/distressing limits W,- W, (highly weathered), W-, (moderately weathered) and W, (slightly weathered) should also be
given along RDs.

3 The gaps should be stuitably filled in giving information about drift.

4 For purpose of representation a uniform height of drift should be assumed.

5 The wall of the drift which the geological cross-section represents should be specified.

6 The horizontal and vertical scales used should be specified.

Fig. 3 A Generalized Geological Longitudinal Section of the Wall of
A Drift in a Geologically Simple Environment

3D GEOLOGICAL LOG OF EXPLORATORY DRIFT

LEFT INVERT

RIGHT INVERT
RD(m) [

T r

ROCK Type

tue. ORIEHTATKIM

awamdiwofjoisg

*>eKTUBanUJNO

TtTBnsiEiniirar

mas'

■BtUbgmarj&BTT

«Ham"«wuwo

XVft.dltKNtAfiaN

-BBBBWirensHrr

tfCTnjRtfmNo

R.O-P.W

tomftweKCLMn

HBlWIWI

glOTITESCHST

MODBmEI.Y WEATHERED

UeOIUMSTWONO

I SlrOKRY V»tATHERED~

^IPCjWS

ROUOH UWOUATOfW

i-i mm CRUSHED HOCK

2-ia mm CXU8HED BOCK

2^aOein I

KXMH UHDUIATOBV. MOW STAIWINP

TIOHT-tnwemBHEDBOCK I

TIGHT.IOitoCHUSHEDROCK

HOUOH IBRgQUtAH

TIOHT-t nun CtlUSHeO ROCK

ROUiHIRreOUU*

a.Sll»nCWU8HEa«0CK

«tjt

M.CLAt»lll (FAIR ROCK)

8D, OASSJI IfAlR WOOO

UNaUPPOKTS)

1.8 m I I

RattmgJm
tlwMor

11m

INDEX

"S'^:^
S^S

2::!^

^

^

^

p^??

e

BIOTTTE SCHIST

CRUSHED ROCK / SHEAR ZONE / SHEAR SEAM
TRACE OF DISCONTINUITY WITH ORIEMTATION
CRUSHED ROCK FILLED DISCONTINUITIES (Mmm)
CRUSHED ROCK FIOEO DISCONTINUITIES (WOmm)

Cl>y FILED JOINT

81 PIANE D^ININQ DRIFT GEOMETRY

SECONDMiY INFtLUNQ (QUARTZ) AU3N0 THE JOVfT

S2 PLANE DEFINING DRIFT GEOMETKV
WAtCR SEEPAGE

Fig. 4 Typical Example of a Three-Dimensional (3D) Geological Log of Exploratory Drift

en

IS 4453 : 2009

Index

Quartzite (White)

Quartzitic Shale (Thickly Bedded)

Thinly Bedded State

F-1 , F-2, etc, indicate faults

Q-1 , Q-2, etc, indicate quartzite (white).

SL-1. SL-2, etc, indicate quartzitic shale.

NOTE — No ground water was encountered in the shaft up to the depth illustrated.

Fig. 5 A Typical Example of Three-Dimensional (3D) Log of a Shaft

18 4453:2009

ground-water level, water inflows during
excavation or any other information bearing
on the ground-water conditions, such as
pumping record of percolation tests .
d) Record of material collected for testing —
The points from which samples were taken,
date and methods of sampling, purpose of
sampling and by whom should be recorded.
Sufficient information should be given on

the samples to permit their ready
identification at a future date. The name of
project, dam site pit or drift number, date, depth
and other pertinent information should be
indicated. Each sample bag or container
should be provided with two tag cards
showing these particulars. One tag should be
put inside and the other outside the bag or
container.

ANNEX A
(Clause 7.2)

LOG OF TEST PIT FOR BORROW AND FOUNDATION INVESTGATIONS

Feature Project TestPitNo

Area Designation Co-ordinates Ground Elevation Depth of Ground Water Level"

Method of Excavation Approximate Dimensions of Hole Dates of Excavation

Hole Logged by

Classification
Symbol

Depth

(m)

Size

and

Type

of

Sample

Taken

Classification
and Description

of Material
(Give Geological

and In-place
Description for

Foundation
Investigation) "

Volume

of Hole

Sampled

(m^

Weight

ofOto

75 mm

Material

in
Sample

(kg)

Percentage
by Volume

of0to75
mm

Material^'

Weight
of 75 to
125 mm
Material

in
Sample

(kg)

Percentage

by Volume

of 75 to

125 mm

Material"

Weigbt
of Plus
125 mm
Material

in
Sample

(kg)

Percentage
by Volume
of Plus 125

mm
Materiap)

Location
of/n-
siOi
Tests

Letter/Graphic

Remarks:'"

1 ) Record after water has reached its natural level.

2) This may be done as given in IS 1498.

3) (Weight of rock sampled x 100)

(Bulk specified gravity of rock) x (Volume of hole sampled)

4) Record water test and density test data, if applicable, and also bulk specific gravity stating how obtained (measured or
estimated) under remarks.

GMGIPN— 143 BISMOKI»^300

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This Indian Standard has been developed from Doc No.: WRD 05 (448).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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